Merkley, D-Ore., spent much of his time going through Gorsuch's record on the bench and talking about the importance of appointing moderate judges to the highest court in the country.
Many Democrats say they believe Gorsuch is too extreme in his strict interpretations of the Constitution to serve on the Supreme Court.
They point to cases in which he sided with employers over employees and ruled in favor of allowing private companies to claim religious exemptions from providing contraception insurance coverage to employees.
"I'm here at 4:20 in the morning because so much is at stake in terms of the legitimacy of the court," Merkley said as he stood on the floor surrounded by a few charts to help keep him on track.
Around 6:30 a.m., Sen. Dick Durbin, D-Ill., arrived in suit and tie to offer some backup for Merkley. He asked his colleagues questions, and the two bantered.
Merkley began his marathon speech around 6:45 p.m. Tuesday and yielded the floor around 10 this morning, more than 15 hours later.
Democrats have the votes to continue debate on confirming Gorsuch under current rules and expect to make a show on the Senate floor this week. For now, 60 votes are needed to end debate, or what's known in Senate parlance as a cloture vote, but Majority Leader Mitch McConnell of Kentucky has vowed to change Senate practice so that the confirmation may proceed with only a simple 51-vote majority.
Changing the rules as McConnell is expected to do has been dubbed the nuclear option, and even some Republican senators do not like the idea. Sen. John McCain, R-Ariz., told reporters Tuesday that anyone who thinks it is good for the Senate in the long term is "a stupid idiot."
When Democrats had the majority in 2013, then–Majority Leader Harry Reid of Nevada also invoked the nuclear option, changing the 60-vote threshold to 51 for Cabinet appointments and judicial nominations below the Supreme Court level.
While Merkley's marathon speech was a galvanizing factor for progressives who oppose Gorsuch's nomination, it had no procedural effect because he did not delay any Senate floor action from moving forward, with the next vote not expected for more than 24 hours.
"The cloture vote will still be on Thursday," McConnell spokesman Don Stewart tweeted overnight.